Current production motor vehicles, such as the modern-day automobile, are originally equipped with a powertrain that operates to propel the vehicle and power the onboard vehicle electronics. In automotive applications, for example, the powertrain is generally typified by a prime mover that delivers tractive force through a multi-speed power transmission to the vehicle's final drive system (e.g., rear differential, axles, and road wheels). Automobiles have traditionally been powered by a reciprocating-piston type internal combustion engine (ICE) assembly because of its ready availability and relatively inexpensive cost, light weight, and overall efficiency. Such engines include compression-ignited (CI) diesel engines, spark-ignited (SI) gasoline engines, flex-fuel models, two, four and six-stroke architectures, and rotary engines, as some non-limiting examples. Hybrid and full-electric vehicles, on the other hand, utilize alternative power sources, such as fuel-cell or battery powered electric motors, to propel the vehicle and minimize/eliminate reliance on an engine for power.
During normal operation of hybrid and electric vehicles (collectively referred to herein as “electric-drive” vehicles), the internal combustion engine (ICE) assemblies and large traction motors generate a significant amount of heat that is radiated into the vehicle's engine compartment. To prolong the operational life of the prime mover(s) and the various components packaged within the engine bay, most automobiles are equipped with passive and active features for managing powertrain temperature. Passive measures for governing excessive heating within the engine compartment include, for example, thermal wrapping the exhaust runners, thermal coating of the headers and manifolds, and integrating thermally insulating packaging for heat sensitive electronics. Active means for cooling the engine compartment include high-performance radiators, high-output coolant pumps, and electric cooling fans. As another option, some vehicle hood assemblies are provided with active or passive air vents designed to expel hot air and amplify convective cooling within the engine bay.
Active thermal management (ATM) systems for automotive powertrains normally employ a central vehicle controller or dedicated control module to regulate operation of a cooling circuit that distributes fluid coolant, generally of oil, water, and/or antifreeze, through heat-producing powertrain components. For standard ICE applications, a coolant pump propels the cooling fluid—colloquially known as “engine coolant”—through coolant passages in the engine block, coolant channels in the transmission case and sump, and hoses to an air-cooled radiator. For early generation hybrid and electric vehicles, the in-vehicle active thermal management system used multiple independent thermal subsystems for cooling discrete segments of the powertrain. Some hybrid electric vehicle (HEV) ATM architectures required a dedicated coolant loop for the engine and transmission, a separate, independently controlled coolant loop for the electric motor(s) and power electronics modules, and yet another distinct coolant loop for regulating battery pack operating temperature. Such an approach is inherently inefficient as multiple independently operated thermal management subsystems require the vehicle be equipped with redundant sets of system components (e.g., a dedicated heat exchanger, a dedicated pump, dedicated valves, etc., for each loop).